<b><i>Introduction:</i></b> Tectal plate gliomas (TPG) constitute a distinct entity of benign tumors of the brain stem which show an indolent clinical course. Adequate treatment of secondary hydrocephalus is undoubtedly a major factor in the outcome. However, little is known about to what degree the tumor itself determines the long-term outcome of these patients. <b><i>Methods:</i></b> We retrospectively analyzed and compared the clinical and radiological data of 16 pediatric TPG patients with data of 12 pediatric idiopathic aqueductal stenosis (IAS) patients treated in our center from 1988 to 2018. For both groups, we assessed the long-term outcome in terms of hydrocephalus management, and for the TPG group, we assessed tumor growth during follow-up. In a separate prospective part of the study, we performed a neuropsychological evaluation in a subgroup of patients using a standardized testing battery, covering intelligence, learning, memory, executive functions, and an inventory on depression. <b><i>Results:</i></b> In the TPG group, the mean clinical and radiological follow-up was 84 and 70 months, respectively. On average, the maximum diameter of the tumor increased by 11% (<i>p</i> = 0.031) and the estimated tumor volume with 35% (<i>p</i> = 0.026) on radiological follow-up. The fronto-occipital horn ratio (FOHR) decreased by 23% on average after treatment. In the IAS group, the mean clinical and radiological follow-up was 117 and 85 months, respectively. In this group, the FOHR decreased by 21% on average. Neurocognitive testing revealed significant higher scores in the TPG group on global intelligence (TPG = 109, IAS = 85.5, <i>U</i> = 3, <i>p</i> &#x3c; 0.01, <i>z</i> = −2.71), performance (TPG= 100, IAS = 85, <i>U</i> = 7, <i>p</i> = 0.03, <i>z</i> = −2.2), and verbal intelligence (TPG = 122, IAS = 91.5, <i>U</i> = 2, <i>p</i> &#x3c; 0.00, <i>z</i> = −2.87) as well as working memory (TPG = 109.5, IAS = 77, <i>U</i> = 0.5, <i>p</i> = 0.01, <i>z</i> = −2.46). <b><i>Conclusion:</i></b> Our results suggest that the long-term outcome in TPG patients is acceptable and that cognition is substantially better preserved than in patients with IAS. This puts the idea of a significant contribution of the tumoral mass to disease outcome on the long term in question. Adequate and prompt management of hydrocephalus is the most important factor in long-term cognitive outcome.